The present invention relates to a semiconductor equipment, and more particularly, to a reference wafer for maintaining laser accuracy and calibrating a camera and a laser of the semiconductor equipment, and a method for fabricating the reference wafer.
As a degree of integration of a semiconductor device becomes higher and a wafer size increases, it is required to precisely control a semiconductor equipment when fabricating the semiconductor device. Particularly, a laser repair equipment used in a process of repairing a semiconductor fuse should focus a laser on an accurate location to cut the semiconductor fuse. However, a failure may occur due to an error of no more than dozens of nanometers according to a device size.
FIG. 1A illustrates a conventional reference wafer for calibrating a semiconductor equipment. FIG. 1B illustrates a plane view of the reference wafer described in FIG. 1A. FIG. 1C illustrates an image of a conventional light reflection layer.
Referring to FIG. 1A, a silicon oxide (SiO2) layer is formed as a first anti-reflection layer 12 on a silicon substrate 11 and Ti/TiN layers 13 and 14 are formed as an adhesive layer on the first anti-reflection layer 12. Then, a tungsten (W) layer is formed as a light absorption layer 15 on the adhesive layer 13 and 14. A silicon oxide (SiO2) layer is formed as a second anti-reflection layer 16 on the W layer 15 and an aluminum (Al) layer is stacked on the second anti-reflection layer 16. Subsequently, an Al pattern is formed as a light reflection layer 17 by performing a masking and etching process on the Al layer. It is noted that the light reflection layer 17 may have a cross shape when referring to FIG. 1B.
As illustrated in FIGS. 1A and 1B, a typical repair method is to irradiate a laser 19 in a vertical direction from a detector 18, to two-dimensionally move (for example, in the directions indicated by the arrows 20) the detector 18 several times, to receive a reflected laser 21 to thereby recognize the light reflection layer 17, to find a center of the light reflection layer 17, and to calibrate a coordinate of the laser 19 to a coordinate that is closest to a (0, 0) coordinate, thereby finding an accurate location of a fuse and blowing the fuse in a practical repair process.
Since, however, in the conventional reference wafer, the aluminum pattern, i.e., the light reflection layer 17, has a relatively large gradient when it is formed by etching the aluminum layer as represented by a reference numeral 22 in FIG. 1C, and a reflection angle with respect to an incident angle, the laser is not detected/measured properly. Thus, the laser accuracy is deteriorated.
Further, the scattered reflection of the laser is a concern at a gradient of the aluminum pattern 17 and thus the accuracy is deteriorated.
Moreover, as the laser is irradiated repeatedly onto the aluminum layer exposed to the air, the oxidation occurs due to the increase of a temperature on the surface of the aluminum pattern. As a result, a usage period of the reference wafer may become shorter.